This invention relates to color photographic sensitive materials suitable for rapid photographic processing. More particularly, it relates to silver halide color photographic sensitive materials improved in the speed of silver removal by bleaching and fixing (hereinafter referred to simply as "silver removal").
Subsequent to the imagewise exposure of the silver halide color photographic sensitive material, fundamental photographic processing steps to reproduce the image on the photographic material are the color developing step and the silver removing step. In the color developing step, silver halide in the exposed silver halide color photographic sensitive material is reduced to silver by the color developing agent and at the same time the oxidized color developing agent reacts with a color forming agent (coupler) to produce a dye image. Thereafter, the color photographic material undergoes silver removing treatment in the next step in which the silver formed in the preceding step is oxidized by an oxidizing agent (commonly called bleaching agent) and then removed from the photographic material by dissolution by the action of a silver ion complexing agent (commonly called fixing agent), leaving behind a dye image on the photographic material. In the actual photographic processing, the fundamental steps of color development and silver removal are accompanied with other auxiliary steps to maintain photographic and physical qualities of the image or to improve preservability of the image such as, for example, hardening bath to prevent the emulsion layer from becoming too soft during the treatment, stop bath to terminate quickly the developing reaction, stabilizing bath to stabilize the image, and stripping bath to remove the backing coat from the support.
In a procedure now practically employed in the silver removing step, the silver image is oxidized to silver halide in a treating solution containing a ferricyanide as major ingredient and the resulting silver halide is transformed into soluble form in a fixing bath containing sodium or ammonium thiosulfate as major ingredient, whereby it is removed by dissolution in water. The former treating procedure utilizing a ferricyanide as major reactant, although generally powerful in silver removing ability, has disadvantages of requiring two baths and frequently a special construction material for the treating equipment on account of the highly corrosive nature of the ferricyanide. Further, the former procedure has another disadvantage of being liable to stain formation when used in treating print paper and a defect of giving rise to environmental pollution, resulting in serious public hazard.
In order to alleviate the above difficulties, a treating solution containing ferric salt of an aminopolycarboxylic acid has been widely used. The problem in this case is a relatively weak silver removing power which necessitates the use of a large amount of an expensive iron salt of aminopolycarboxylic acid. To overcome the difficulty, the iron salt of an aminopolycarboxylic acid has been used cojointly with a so-called bleach accelerator. Examples of widely known bleach accelerators include thiourea described in Swiss Pat. No. 336,257, thiourea derivatives in Japanese Patent Publication No. 8,506/70, polyoxyethylene compounds in German Pat. No. 966,410, iodine compounds in German Pat. No. 1,127,715, heterocyclic compounds in German Pat. No. 1,290,812, selenium compounds in Brit. Pat. No. 1,217,194, alkylamine compounds in Brit. Pat. No. 1,192,481, polyamine compounds in Japanese Pat. Publication No. 8,836/70, and other compounds disclosed in U.S. Pat. Nos. 3,042,520, 3,241,966, 3,983,858, Japanese patent application Laid-Open ("Kokai") Nos. 40,943/74, 59,644/74, 117,037/74, 88,522/74, 42,349/74, 110,327/76, Brit. Pat. No. 926,569, 1,170,973, 1,201,571, and German Pat. No. 1,937,727.
Most of the known accelerators, however, are insufficient in accelerating effect and tend to lose the effectiveness during storage of the treating solution. Others, even though sufficient in effectiveness, have also unsatisfactory properties of some kind or other such as causing undesirable fogging by contaminating other treating solutions (for example, developing bath) as in the case of automatic processing by means of an automatic processing equipment in which contaminants tend to be carried by the belting or the like to other treating baths to contaminate them.
On the other hand, in recent years, there have been ever increasing demands for the color photographic sensitive materials which can be photographically processed more rapidly and demands for those which contain silver halide in an amount as small as possible in order to save silver resources. so-called thinning of emulsion layers, that is, reduction in the thickness of emulsion layers, is advantageous for the rapid processing because of rapid silver removal and for other reasons, but has its own limit. Consequently, several means have heretofore been proposed to meet the above demands. Firstly, couplers of the two equivalent type, particularly two equivalent yellow couplers and two equivalent magenta couplers in recent years, have been commercialized and in actual use. As compared with conventional couplers of the four equivalent type, the two equivalent type allows the amount used of silver halide to be reduced to from two-thirds to one half as well as the photographic processing to be carried out more rapidly, but sometimes accompanies difficulty in silver removal. Secondly, a developing agent of high developing activity such as, for example, 4-amino-3-methyl-N-ethyl-N-methoxyethylaniline or p-aminophenol has been used. In this case, the rapidity of processing depends on the speed of silver removal. Thirdly, where has been proposed a means whereby a color photographic image can be obtained with a sensitive material of extremely low silver halide content by incorporating in the processing procedure an image intensifying operation utilizing complex cobalt salts or peroxides as described in, for example, Japanese patent application Laid-Open ("Kokai") Nos. 9,728/73, 9,729/73, 48,130/73, 64,932/73, 23,634/74, 84,229/74 and 84,239/74. However, in this case also simplification and speed-up of photographic processing encounter a difficulty in the silver removing step.
As described above, the greatest difficulty encountered in exploiting a silver halide color photographic sensitive material suitable for rapid photographic processing exists in silver removal. Although there are a few proposals for improving the silver removability of the color photographic sensitive material itself [for example, Japanese patent application Laid-Open ("Kokai") Nos. 19,750/69, 49,725/76 and 110,327/51], the fact is that most of the current color photographic techniques owe the silver removal to the processing steps, particularly the bleaching or bleachfixing bath containing the aforementioned bleach accelerators or the like. It is not unconceivable that some of the known bleach accelerators might possibly promote the silver removal more effectively when incorporated in at least one layer of the silver halide color photographic sensitive material, preferably in a non-sensitive layer adjacent to the silver halide emulsion layers in order to reduce the photographic influence than when present in a processing bath such as bleaching or bleachfixing bath. However, when directly incorporated in a color photographic sensitive material, many of the compounds commonly called bleach accelerators bring about undesirable fog and such compounds generally affects adversely the photosensitivity of the fresh sensitive material and photographic characteristics (sensitivity, gradation, fog, etc.) of the preserved sensitive material. For these reasons, the inclusion of a bleach accelerator in the sensitive material has heretofore been precluded from actual use. Even if compounds suitable for use as internal bleach accelerators might be found, on careful selection such compounds would be very limited in number until future technical improvement might permit the bleach accelerators to be directly incorporated in the sensitive material.